The field of the invention generally relates to optical imaging, and more specifically relates to Optical Coherence Tomography (“OCT”) systems and methods.
Spectral modifications resulting from interference of light in, also known as channeled spectra can be observed with various spectral interferometric techniques, commonly consisting of a nonscanning interferometer and spectrometer in the detection path in OCT systems. The superposition of two light beams that are identical except for a relative optical path-length difference L results in a new spectra with ripples that have minima at wavelength λ whenever (n+½)λ=L. If the optical path length difference is constant over the bandwidth of light, the spacing between the adjacent minima of the resultant spectrum in the optical frequency (v) domain is a constant c/L, where c is the speed of light.
The interference fringes in the spectral domain can be obtained by performing Fourier transform of those recorded in the time domain, distinct differences are recognized between these two measurements. When the optical path length difference between two interfering beams, L=c τ, of the source light is much greater than the source temporal coherence length, high visibility interference fringes are not observed in the time domain. In the spectral domain, however, high visibility fringes are formed irrespective of how long or short the optical path-length difference may be. Additionally, superior sensitivity and signal to noise ratio of spectral interferometry over time-domain approaches are recognized.
Channeled spectra recorded by spectral interferometers have been used to measure absolute distance, dispersion, and both absolute distance and dispersion. By analogy with a two-beam interferometer, the two axes of an optically anisotropic sample or optical fiber can be regarded as two beam paths, while a polarizer placed at the exit end of a sample under test or optical fiber can superpose light from the two beam paths to generate interference fringes in the spectral domain. In practice, polarization control is difficult to realize, since the polarization-mode dispersion in fiber is random and the polarization transformations introduced by fiber components are not common for light in reference and sample paths. Therefore, at the output of the fiber-based polarization-sensitive Michelson, Mach-Zehnder or similar hybrid interferometers, recorded interference fringe signals may contain an unknown time-varying random phase factor due to polarization changes induced by fiber components.
The embodiments described herein solve these problems, as well as others.